Heat packs of various types have long been used in the medical field and by sportsmen for the purpose of applying heat to localized areas of the body to alleviate stiffness or minimize tissue damage due to freezing, for example.
Heat packs employing hot water or electrically-generated heat suffer from certain disadvantages in convenience of use. These disadvantages have been overcome by the use of super-saturated salt solutions inside sealed containers that are activated to crystallize and thereby generate heat. The temperature achieved by such devices can be controlled based upon the type of salt used and its concentration. When the crystallization is complete, the salt is returned to its super-saturated condition by heating the sealed container in hot water, by microwave radiation, or by other heat sources.
The activation of super-saturated salt heating pads is carried out by the flexing of a metal disk that contains slits through its thickness. The slits may start at the edge of the metal disk and terminate in its interior, or they may be entirely within the interior of the disk. It has been theorized that these metal disks initiate crystallization by presenting at the termini of the slits new metal surfaces that are created by the flexing of the metal disk. In some metal disks, the disks are roughened after the slits are formed, this roughening producing minute nodules of metal on the disk. It is theorized that these roughened metal disks release some of these nodules when the disk is flexed, and that the nodules are responsible for initiating crystallization. Further information about these disks and the super-saturated salt solutions that they activate is available from U.S. Pat. Nos. 4,077,390 to Stanley et al., 4,572,158 to Fiedler, and 4,872,442, 4,880,953, and 5,058,563 all to Manker, the entire disclosures of which are hereby incorporated by reference.
The application of heat to the human female breast prior to and during expression results in improved comfort to the woman. It also may enhance letdown, relieve engorgement and soften the areola. Additionally, heat increases the blood flow to the tissue, thereby improving the woman's comfort and the activity of the breast tissues. Finally, the comfortable feelings derived from the application of heat to the breast tends to exert a calming effect and relieve stress in the woman, both of which increase the chances of successfully feeding of the infant or the expression of milk through use of a breast pump or hand expression.